In recent years, processes of compressing moving picture data highly efficiently based on interframe prediction and transmitting the encoded data produced by the highly efficient compression have widely been used as processes of efficiently transmitting moving picture data. According to these processes, predictive parameters obtained by predicting encoded images from chronologically successive frames and predicted residual image data are encoded thereby to reduce the amount of information of highly chronologically correlated moving picture data. The predicted residual image data are highly efficiently compressed by a converting/encoding process and a quantizing process, making it possible to transmit moving picture data in a small transmission band.
One example of such processes is a process using a compression encoding scheme such as MPEG (Moving Picture Expert Group)-1, MPEG-2, or MPEG-4. According to these compression encoding schemes, an input image frame is divided into rectangular areas of constant size, called macroblocks, and an interframe prediction is performed in each of the rectangular areas based on motion compensation, and motion vectors and predicted residual image data that are obtained are processed by two-dimensional discrete cosine transform and quantization to convert compressed signal data into a variable length code.
According to conventional moving picture transmission processes, however, if a transmitted data error or a transmitted packet loss which is in the form of a long burst that cannot be recovered even by an error-correcting code occurs, then the recipient is unable to properly recover the image data of the frame which has suffered the error.
One countermeasure that the recipient can take to protect against such errors is an error concealment process for generating image data in a manner to cover up an error, from image data of frames that exist chronologically before and after the error frame and that have been properly decoded, and image data that exist around the error region within the error frame. However, it is impossible to remove decoded image corruptions even with the error concealment process. Moreover, since the error concealment process relies upon the interframe prediction, an image corruption that has occurred once is propagated to succeeding frames.
When information is distributed by multicasting/broadcasting, data error information or packet loss information of received data cannot be transmitted from the recipient to the sender. If error information is transmitted by return from the recipient to the sender, then the feedback information occupies the band of the communication path.